Catalytic rearrangement of alkyl aromatics

ABSTRACT

IN THE CATALYTIC REARRANGEMENT OF ALKYL AROMATICS OVER A CATALYST OF A HYDROGENATING COMPONENT OR AN ALKALICATION DEFICIENT ZEOLITE, THE FEEDSTOCK CONTAINS LESS THAN 0.5% WT., PREFERABLY LESS THAN 0.1% WT. OF NON-AROMATIC HYDROCARBONS SO THAT THE CATALYST ACTIVITY IS INCREASED. THE PREFERRD ZEOLITE IS DECATIONISED MORDENITE AND THE PREFERRED HYDROGENATING COMPONENT A GROUP VIII METAL E.G. NICKEL ADDED BY ION-EXCHANGE. THE OPERATING CONDITIONS MAY BE 300-525*C., 0-1500 P.S.I.G., 0.1-10 V./V./HR. 1,000-15,000 S.C.F. H2/B. PARAFFINS WERE FOUND TO BE A PERMANENT AND NAPHTHENES A TEMPORARY POISION FOR THE CATALYST.

United States Patent 3,629,351 CATALYTIC REARRANGEMENT 0F ALKYLAROMATICS Martin Frederick Olive, Lightwater, and Geoffrey Dovey,

Shepperton, England, assignors to The British Petroleum Company Limited,London, England No Drawing. Filed Dec. 16, 1969, Ser. No. 885,627 Claimspriority, application Great Britain, Jan. 15, 1969, 2,405/ 69 Int. Cl.C07c 3/00, 15/08 US. Cl. 260-672 T 8 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to the catalytic rearrangement of alkyl aromaticsover zeolite catalysts.

Various rearrangements of alkyl aromatics are known to be possible andto be catalysed by acidic catalysts, particularly disproportionation(e.g. the conversion of toluene to benzene and xylenes) but alsoisomerisation (e.g. the alteration of the proportions of xylene isomersin a mixture) and transalkylation (e.g. the interaction of xylenes andtoluene to give tri-methyl benzenes and benzene). It is also known thatcertain zeolites will catalyse these reactions.

It has now been found that the presence of non-aromatic hydrocarbons inan alkyl aromatic feedstock has a marked effect on the activity ofzeolite catalysts. Alkyl aromatics are obtained on a commercial scale byseparation from hydrocarbon mixtures containing them, particularly bythe solvent extraction of catalytic reformates and steam crackergasolines which have been hydrogenated to convert olefins to paraffins.In such commercial separations small amounts of non-aromatichydrocarbons can and do appear in the alkyl aromatic portion, but it hasnow been found that these non-aromatics should be kept to a minimum.

According to the present invention therefore a process for the catalyticrearrangement of alkyl aromatics comprises contacting an alkyl aromaticfeedstock having a non-aromatic hydrocarbon content of less than 0.5 wt.at elevated temperature and pressure and in the presence of hydrogenwith a catalyst comprising an alkali metal cation deficient zeolitehaving pores of at least 6 A. and a hydrogenating component selectedfrom the metals of Groups I-B, V-A, VI-A, VIIA and VIII of the PeriodicTable according to Mendeleeff.

Preferably the non-aromatic hydrocarbon content of the feedstock is lessthan 0 .1% Wt. The non-aromatic hydrocarbons normally present incommercial alkyl-aromatic feedstocks are paraffins and naphthenes butolefins may also be present. It has been found that paraflins are moredeleterious than naphthenes since parafiins appear to deactivate thecatalyst permanently. Naphthenes lower the catalyst activity if presentbut the activity is at least partially restored when the naphthenes areremoved. The content of non hydrocarbon components e.g. sulphurcompounds is also preferably less than 0.1% wt.

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The feedstocks having the above mentioned low nonaromatic hydrocarboncontent may be produced in any known manner. As indicated above the mostcommon method of producing alkyl aromatics of high purity is by theextraction of alkyl aromatics from hydrocarbon mixtures containing themusing a selective solvent for the aromatics. Various commerciallyavailable solvent extraction processes exist, the most common solventsbeing alkylene glycols, sulpholanes, N-alkyl pyrrolidones and furfural.The term solvent extraction is to be understood as including extractivedistillation. As is also known, the operating conditions for suchprocesses e.g. temperature, temperature gradient in the extractioncolumn and solvent: hydrocarbon ratio can be varied to control the yieldand purity of the aromatics produced. Samples from a commerical solventextraction process have, for example, been analysed and found to have apurity of 99.95% wt., so there is no problem, in practice, of reachingthe levels specified above. Other methods of producing the feedstocksrequired, which may be used in combination with solvent extraction ifdesired are distillation, and molecular sieve extraction.

Preferred feedstocks contain C7-C15 alkyl aromatics, particularly C -Calkyl aromatics, and more particularly, toluene. However alkylderivatives of naphthalene having 1 to 5 carbon atoms in alkyl sidechains may also be treated. The feedstock may be a single alkyl aromaticor mixtures thereof.

The preferred reaction is disproportionation. Since disproportionation,transalkylation and isomerisation are all believed to be carbonium ionreactions more than one reaction may occur in any given system. Thebroad ranges of conditions and preferred conditions tending to givedisproportionation are set out in Table 1 below.

Pressure, p.s.i.g 0-1, 500 Space velocity, v./v./hr 0.1-10 1, 000-15,000

0. 5-4 Hydrogen gas rate, s.c.t./b 4, 000-12, 500

There may also be some dealkylation. However, it is believed thatdealkylation proceeds via a different mechanism from rearrangementreaction and is not likely to be markedly affected by the content ofnon-aromatic hydrocarbons in the feedstock.

The zeolite used in the catalyst is preferably mordenite, although otherzeolites with pores greater than 6 A. may be used if desired e.g.faujasite or Zeolite Y and Zeolite L. In their normal form zeolites havea rigid network of aluminum, silicon and oxygen atoms together withmetal cations which are interchangeable. In freshly prepared syntheticzeolites or natural Zeolites these are usually alkali metal cations.These alkali metal cations can be exchanged for other metal cations e.g.Group 11 metal cations or for hydrogen or ammonium cations and the termalkali-metal cation deficient zeolite as used in this specificationpreferably means a zeolite with an alkali metal content of less than 2%wt, more particularly less than 1.0% wt.

The alkali metal cations normally present may be replaced for example byGroup II metal cations e.g. calcium or magnesium or by rare earth metalions but preferably a decationised zeolite is used. Decationisedzeolites are sometimes referred to as hydrogen zeolites, it beingassumed that the ion balance is maintained by hydrogen ions.Decationisation can be achieved by exchange of the alkali metal cationswith ammonium ions followed by heating at e.g. 250600 C. to drive offthe ammonia.

With this method of decationisation alkali metal contents can be reducedto less than 0.5% wt. An alternative method is treatment with an acid todecationise the zeolite directly. Suitable acids are hydrochloric orsulphuric acid. A combination of ammonium and acid treatment in eitherorder may also be used. Both ammonium and acid treatment have been foundto give active catalysts and it appears that the most important factorin activity is the residual alkali metal cation content, which ispreferably as low as possible. In general it has been found thatammonium treatment gives the lowest residual metal cation content.

Desirably the zeolite has a SiO :Al O ratio of at least 3 :1 since thehigher the ratio the more stable is the zeolite to decationisation andto acids. If the acid treatment uses strong acid of from 5-50% wt.strength, preferably wt. strength, an additional effect is obtained,particularly with the preferred Zeolite, mordenite, in that aluminium isremoved from the crystal lattice with a consequent increase in thesilicazalumina ratio. With mordenite, for example, the normalsilicazalumina ratio of 9-1111 can be substantially increased (SiO :AlO- ratios of as high as 90:1 have been reported) without alteration ofthe physical characteristics of the zeolite.

After either form of decationisation the zeolite is desirably washed toremove excess acid or ammonium exchange solution and is heated to 250600C.

The hydrogenating component is preferably a Group VIII metal, forexample an iron group metal, particularly 4 water at ambient temperatureand then dried for 4 hours at 110 C.

The finished catalyst had the following analysis Ni0.77% wt.

Si-40.0% wt.

SiO :Al O ratio-41.52% Wt. Na0.69% Wt.

Surface area-408 m. g. Pore volume0.22 ml./ g.

The catalyst, after calcination in air at 500 C. for 3 hours andreduction in hydrogen at 450 C. for 2 hours, was used todisproportionate toluene in an extended run The toluene feedstock wasobtained from a commercial solvent extraction plant. Small changes inthe feedstocks and operating conditions produced variations in theparafiin and naphthene contents. Variations in such contents were alsoobtained by the addition of parafiins and naphthenes to the feedstock.The effect of these variations on catalyst activity was assessed duringthe run and the recobalt or nickel, or a platinum group metal,particularly sults are show in Table 2 below.

TABLE 2 Hours on stream 0-699 700-1, 467 1, 468-1, 543 1, 544-1, 654 1,655-1, 750 1, 751-2, 063 2, 064-2, 133 2, 134

Feedstock percent wt.:

Total parafiins and naphthenes" 1. 43 0.06 1. 43 0. O6 0. 9!) 0. 49 1.49 0.49 Isa-octane 0. 5 Methyl cyclohexano 1.0 Toluene 98. 47 99. 62 98.47 90. 02 93. 84 99. 98. 42 99. 35 Other aromatics 0.10 0.32 0.10 0.320.17 0.16 0. 09 0. 16 Toluene conversion, percent wt 43 47 43 44. 5 4343 39. 5 42 Product, percent wt.:

Benzene 19. 4 21. 0 18. 7 18.8 10.1 18. 7 16. 2 17. 0 Xylenes 19. 5 21.6 20.0 21.2 20.1 20. 6 19.1 20. 4

*The parafiin and naphthene contents were measured by gas-li uidchromatography.

platinum or palladium. It may also be a Group IB metal (i.e. copper,gold, or, particularly, silver). It may be present in an amount from0.15% wt., particularly 0.5- 2.0% wt., and it is preferably added by ionexchange, thereby taking up at least a part of the alkali metal cationdeficiency. It is preferably incorporated into the alkalimetal deficientZeolite e.g. after decationisation, although it may be incorporatedbefore the heating to drive off ammonia and/or water. Certain of thehydrogenatnig metals, particularly the Group V-A metals (i.e. vanadium,niobium and tantalum) and the Group VI-A metals (i.e. chromium,molybdenum and tungsten) are not readily incorporated into zeolites byion-exchange and these metals may be present at least partly asimpregnated metals. The Group VIIA metals are manganese, masurium andrhenium.

The catalyst may be reduced in a stream of hydrogen at 250-600 C. beforeuse.

The invention is illustrated by the following example.

EXAMPLE A decationised mordenite was prepared by refluxing 150 g. ofsodium mordenite with 50 g. of ammonium nitrate in one litre ofdeionised water for 4 hours. The mordenite was filtered, thoroughlywashed with deionised water and dried at 110 C. for 4 hours.

Nickel was exchanged onto the decationised mordenite by refluxing with asolution of 4.75 g. nickel nitrate, Ni(NO 6H O, in 250 m1. deionisedwater for 18 hours. The resulting catalyst was washed with 6 liters ofdeionised From the first 4 columns of Table 2 it will be seen that thetoluene conversion was markedly affected by the amount of parafiins andnaphthenes in the feedstock.

In columns 5 to 8 the relative effect of parafiins and naphthenes wasinvestigated. In column 5, 0.5 wt. of iso octane was added to afeedstock already containing 0.49% wt. of paraflins and naphthenes(giving a total 0.99). As expected the conversion dropped, and it didnot increase again when the addition of the iso octane was stopped(column 6). In column 7, 1.0% wt. of methylcyclohexane was added to thesame feedstock and again the conversion dropped. However in thisinstance the activity improved when the addition of the naphthene wasstopped (column 8).

We claim;

1. A process for the catalytic rearrangement of alkyl aromaticscomprising contacting an alkyl aromatic feedstock having a non-aromatichydrocarbon content of less than 0.5% wt. at a temperature of from 300to 525 C. and a pressure of from 0 to 1500 p.s.i.g. and in the presenceof hydrogen with a catalyst comprising a zeolite having pores of atleast 6 A. and an alkali metal content of less than 2% wt. havingincorporated therewith from 0.1 to 5% wt. of a hydrogenating componentselected from the metals of Groups IB, V-A, VI-A, VII-A and VIII of thePeriodic Table according to Mendeleeff, and maintaining the non-aromatichydrocarbon content of said feedstock at less than said percent wt.during the contacting operation.

2. A process as claimed in claim 1 wherein the nonaromatic hydrocarboncontent of the feedstock is less than 0.1% wt.

3. A process as claimed in claim 1 wherein the feedstock is toluene.

4. A process as claimed in claim 1, wherein the process is carried outat 350 to 500 C. and 150 to 1000 p.s.i.g.

5. A process as claimed in claim 1 wherein the zeolite is mordenite.

6. A process as claimed in claim 1 wherein the zeolite has an alkalimetal content of less than 1% Wt.

7. A process as claimed in claim 1 wherein the hydrogenating componentis present in an amount of from 0.5 to 2% Wt.

8. A process as claimed in claim 1 wherein the hydrogenating componentis nickel.

References Cited UNITED STATES PATENTS Benesi et a1. 260672 Wise 2'60668Pollitzer 260672 Pollitzer 260672 Pollitzer 260-672 Brandenburg et al.260672 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,629,351 Dated D c r 21', 1971 Inventor) Martin Frederick Olive andGeoffrey Dovey It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Col. 1, Line 2 3, I for 'v/v/hr. I read v/v/hr,

Col. 2, Line 47, for "reaction" I I read reactions Col. 3, Line 52, for"hydrogenatnig" read,

hydrogenating Col. 4, Line 5, v Q for "6:77," read 6. 77

Signed and sealed this 13th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTISCHALK Attesting Officer Commissionerof Patents

